mysterious transient objects poonam chandra royal military collage of canada
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Mysterious transient objects
Poonam ChandraRoyal Military Collage of Canada
Universe has > 125 billion galaxiesEach galaxy has ~100 billion stars
Astronomical time scales•Age of Universe ~14 billion years•Life time of stars ~ millions to billions of years
Some sources appear in the sky for few seconds to few months to few years…. Transient objects
Observing, modeling and understanding these transient objects
SUPERNOVAE (SNe)
Few months to few years timescaleMassive explosions in the universeEnergy emitted 1051 ergs (1029 times more than an atmospheric nuclear explosion)Shines brighter than the host GalaxyAs much energy in 1 month as sun in ~1 billion yearsIn universe 8 supernova explosions every second Thermonuclear and gravitational collapse
GAMMA-RAY BURSTS (GRBs)
Most luminous events in the universe since big bangFlashes of gamma-rays from random directions in skyFew milliseconds to few seconds timescaleEven 100 times more energetic than supernovaeBrightest sources of cosmic gamma-ray photons in the universeIn universe roughly 1 GRB is detected per dayShort duration (< 2 sec) and long duration (> 2sec)
Soft Gamma-Ray Repeaters (SGR)
Time scale of few daysRepeated flares in Soft Gamma Ray or hard X-ray bandLess energetic then supernovae and GRBs but GalacticIn 1/10 of a second as much energy as sun emits in 100,000 years continuously.1000 times more bright than combining all the stars of Milky Way together.Only handful of SGRs are known
Common origin: Massive stars
Nuclear reactions inside a star
4-8 Msun : thermonuclear supernovae
•4-8 Massive star: Burning until Carbon•Makes Carbon-Oxygen white dwarf•White Dwarf in binary companion accretes mass•Mass reaches Chandrashekhar mass•Core reaches ignition temperature for Carbon•Merges with the binary, exceed Chandrasekhar mass•Begins to collapse. Nuclear fusion sets•Explosion by runaway reaction – Carbon detonation• Nothing remains at the center• Energy of 1051 ergs comes out• Standard candles, geometry of the Universe
Thermonuclear Supernovae
M >8 Msun : core collapse supernovae
• Burns until Iron core is form at the center• No more burning• Gravitational collapse• First implosion (increasing density and temperature at the center)• Core very hard (nuclear matter density)• Implosion turns into explosion• Neutron star remnant at the centre.• Explosion with 1053 ergs energy• 99% in neutrinos and 1 % in ElectroMagnetic• Scatter all heavy material required for life
Core Collapse
Supernovae
M > 30 Msun : Gamma Ray Bursts
• Forms black hole at the center•Rapidly rotating massive star collapses into the black hole.•Accretion disk around the black hole creates jets•GRBs are collimated.• All GRBs extragalactic• Some GRBs associated with supernovae (GRB980425/SN1998bw, GRB030329/SN2003dh etc.)• Dedicated instruments (BATSE, BeppoSax, Swift)• These GRBs last for few seconds • For longer duration in lower energy bands
Short Hard Bursts
•Neutron stars or black holes formed during end stages of massive stars
•Merger of two neutron stars or a black hole and a neutron star colliding
•Less energetic than collapsar GRBs
•Duration less than < 2 seconds.
Soft Gamma Ray Repeater
•When the neutron star in initial formation stages gains very high magnetic field•It becomes a magnetar with 1015 Gauss magnetic field•Global rearrangement in its magnetic structures give SGRs•Only Galactic sources with energies ~1041-46 ergs
Ic
dlB 4
.
One common origin
DEATH OF MASSIVE STARS
•How do massive stars die?•How are these extreme conditions reached in these events? •Does the known physical laws work in these extreme conditions? •Why does small difference in initial conditions lead to such drastic differences? •Does nature really need so much fine tuning?
Specific problems:
Shock velocity of typical SNe are ~1000 times the velocity of the (red supergiant) wind. Hence, SNe observed few years after explosion can probe the
history of the progenitor star thousands of years back.
Interaction of the ejected material from the supernovae and GRBs with their surrounding medium and study them in multiwavebands.
SN/GRB explosion centre
Photosphere
Outgoing ejecta
Reverse shock shell
Contact discontinuity
Forward shock shell
Circumstellar environment
105K
109K107K
Radio emission is synchrotron emission due to energetic electrons in the presence of the high energy magnetic fields.
Radio emission is absorbed either by free-free absorption from the circumstellar medium or
synchrotron self absorption depending upon the mass loss rate, ejecta velocity and electron temperature, magnetic field. Both absorption mechanisms carry
relevant information.
Radio Emission
Free-free absorption: absorption by external medium
Information about mass loss rate.
Synchrotron self absorption: absorption by internal medium
Information about magnetic field and the size.
32
3
2
2.
Rw TuM sff
NB relssa
5.15.2
X-ray emission from supernovae
Thermal X-rays
versus
Non-thermal X-rays
Date of Explosion : 28 March 1993
Type : IIb
Parent Galaxy :M81
Distance : 3.63 Mpc
SN 1993J
“Modeling the light curves of SN 1993J”, T. Nymark, P. Chandra, C. Fransson 2008, accepted for publication in A&A
“X-rays from explosion site: 15 years of light curves of SN 1993J”, P. Chandra, et al. 2008, submitted to ApJ
“Synchrotron aging and the radio spectrum of SN 1993J”, P. Chandra, A. Ray, S. Bhatnagar 2004 ApJ Letters 604, 97
“The late time radio emission from SN1993J at meter wavelengths”, P. Chandra, A. Ray, S. Bhatnagar 2004 ApJ Letters 604, 97
Understanding the physical mechanisms in the forward shocked shell from observations in low and high frequency radio bands with the GMRT and the VLA.
Radio emission in a supernova arises due to synchrotron emission, which arises by the
ACCELERATION OF ELECTRONS
in presence of an
ENHANCED MAGNETIC FIELD.
Giant Meterwave Radio Telescope, India
Very Large Array, USA
On Day 3200…… GMRT+VLA spectrum
GMRT
VLA
Synchrotron
cooling break at 4 GHz
Chandra, P. et al. 2004
Frequency
Flux
1.5 years later…………. ~Day 3750
Synchrotron cooling break at
~5.5 GHz
GMRT
VLA
Frequency
Flux
Synchrotron Aging
Due to the efficient synchrotron radiation, the electrons, in a
magnetic field, with high energies are depleted.
tbBE offcut 2
1
bN
(E)
E
N(E)=kE-g
.
Q(E)E-g
steepening of spectral index from a=(g-1)/2 to g/2 i.e. by 0.5
.
253
sin4
3EB
cm
e
22274
4
sin3
2EB
cm
e
dt
dE
Sync
On day 3200
B=330 mG
On day 3770
B=280 mG
Magnetic Field follows 1/t decline trend
Equipartition magnetic field~ 30 mG
Equipartition magnetic field is 10 times smaller than actual B, hence magnetic energy density is 4 order of magnitude higher than relativistic energy density
2/12/32
2/12/12
30 2
202
20tt
Rtt
RB
dt
d break
Diffusion acceleration coefficient
k=(5.3 +/- 3.0) x 1024 cm2 s-1
On Day 3200…… GMRT+VLA spectrum
GMRT
VLA
Synchrotron
cooling break at 4 GHz
Chandra, P. et al. 2004
Frequency
Flux
X-ray studies of SN 1993J (Chandra et al 2008; Nymark, Chandra, Fransson 2008)
ROSATASCAChandraXMM-NewtonSwift
X-ray telescopes
ROSAT SwiftASCA
Chandra
XMM
X-ray studies of SN 1993J (Chandra et al 2008; Nymark, Chandra, Fransson 2008)
L ~ t-(0.8-1): adia
L ~ t-1/(n-2): rad.
Density index ~ 12
X-ray spectrum of SN 1993J (Chandra et al 2008; Nymark, Chandra, Fransson 2008)
CONCLUSIONS
•All the X-ray emission below 8 keV is coming from reverse shock.•Reverse shock is adiabatic and clumpy.•The clumps are producing slow moving radiative reverse shock.•The ejecta density profile is Density ~ R-12
•The reverse shock has travelled upto CNO zone in the ejecta.
SN 1995N in radio and X-ray bands (Chandra et al 2008, to appear in ApJ;
Chandra, P. et al. 2005, ApJ)
SN 1995N A type IIn supernova
Discovered on 1995 May 5
Parent Galaxy MCG-02-38-017 (Distance=24 Mpc)
Bremsstrahlung (kT=2.21 keV, NH=2.46 x 1021/cm2. )
Gaussians at 1.03 keV (N=0.34 +/- 0.19 x 10-5) and 0.87 keV (N=0.36 +/- 0.41 x 10-5)
NeXNeIX?
NeX
NeIX
99.9%90%67%
99.9%90%67%
Constraining the progenitor mass
4NeXeff
NeXIe
NeXNeX
hnn
dVdjL
2
1
51077.6
f
ne
sunNe MM 016.0Compatible with 15 solar mass progenitor star
Luminosity of Neon X line
Cascade factor
Emissivity of neon X line
Number density of neon is ~ 600 cm-3.
Fraction of NeXI to total Neon
SN 1995N Chandra observations
Total counts 758 counts
Temperature 2.35 keV
Absorption column
Depth 1.5 x 10-21 cm-2
0.1-2.4 keV
Unabsorbed flux 0.6-1.0 x 10-13 erg cm-2 s-1
0.5-7.0 keV
Unabsorbed flux 0.8-1.3 x 10-13 erg cm-2 s-1
Luminosity (0.1-10 keV) 2 x 1040 erg s-1
•How fast ejecta is decelerating? R~t-0.8
•What is the mass loss rate of the progenitor star? M/t = 6 x 10-5 Msun yr-1
•Density structure Density ~ R-8.5
•Density and temperature of the reverse shock Forward shock: T=2.4 x 108 K, Density=3.3 x 105 cm-3
Reverse shock: T=0.9 x 107 K, Density= 2 x 106 cm-3
SN 2006X, Patat, Chandra, P. et al. 2007, Science•Type Ia supernova (Thermonuclear supernova)•True nature of progenitor star system? •What serves as a companion star? •How to detect signatures of the binary system? Single degenerate or double degenerate system?
Observations of SN 2006X: •Observations with 8.2m VLT on day -2, +14, +61, +121 •Observations with Keck on day +105•Observations with VLA on day 400 (Chandra ∼et al. ATel 2007). •Observations with VLA on day 2 (Stockdale, ∼ATel 729, 2006). •Observations with ChandraXO on day 10 ∼(Immler, ATel 751, 2006).
Na I D2 line
Na vs Ca
RESULTS•First ever supernova followed regularly till 4 months.• Variability not due to line-of-sight geometric effects.•Associated with the progenitor system. •Estimate of Na I ionizing flux: SUV 5 × 10 ∼ 50 photons s − 1
• This flux can ionize Na I up to ri 10∼ 18 cm. •This implies ne 10 ∼ 5 cm − 3 (ONLY PARTIALLY IONIZED HYDROGEN CAN PRODUCE SUCH HIGH NUMBER DENSITY OF ELECTRONS )
•Confinement: rH ≈ 10 16 cm •Ionization timescale τi < Recombination timescale τr . Increase in ionization fraction till maximum light. Recombination star ts.• When all Na II recombined, no evolution. Agree with results.
From spectroscopic data: Na I column density N (Na I) ≈ 1012 cm − 1 log(Na/H)= −6.3. For complete recombination, M (H) ≤ 3 × 10−4 M. ⊙
From radio: 3 − σ upper limit on flux density F (8.46GHz) < 70 µJy. Mass loss rate ≤ 10 − 8 M year ⊙ − 1
CSM mass < 10 − 3 M Below detection limit. ⊙
Mass estimation
•CSM expansion velocity 50 − 100 km s ∼ − 1 . •For R 10∼ 16 cm, material ejected 50 year before! ∼•Double-degenerate system not possible. Not enough mass. •Single degenerate. Favorable. •Not main sequence stars or compact Helium stars. •High velocity required. •Compatible with Early red giant phase stars. •Possibility of successive novae ejection.
Nature of the progenitor star
COLLABORATORS
Claes Fransson (Stockholm Obs)Tanya Nymark (Stockholm Obs)Roger Chevalier (UVA)Dale Frail (NRAO)Alak Ray (TIFR)Shri Kulkarni (Caltech)Brad Cenko (Caltech)Kurt Weiler (NRL)Christopher Stockdale (Marquette)…and …. more
•Detected by inter-Planetary Network of GRB detectors•Triangulated by Odyssey, Suzaku, Integral•RHESII, Konus-Wind observed•Swift was slewing, BAT marginal detection at t=4min
•RHESSI: Epeak =980+/-300 keV and•Fluence (30keV-10MeV) =1.5 x 10-4 erg cm-1
•Konus-Wind: Epeak=367+/-~60 keV and•fluence (20keV-10MeV)= 1.74 x 10-4 erg cm-1
•Redshift z=1.5477, Eiso = 1054 ergGCN 6028,6102,6071,6049,6047,6041,6096,6030,6039,6064,6042
GRB 070125: Chandra et al. 2008 ApJ
GRB 070125: observationsObserved by Swift-XRT, Swift-UVOT, P60, SARA 0.9m, Lick 3m, Keck/LRIS, TNT 0.8m, Prompt, VLT, GMRT, WSRT, VLA , IRAM
Follow up Observatiions:
•P60 observations until day ~25•(Swift-XRT followed it until day 14)•Chandra observations on day ~39•Submm observations until day ~15•VLA observations until day ~280
MULTIW
AVEBAND
MODELIN
G OF
BRIGHTEST R
ADIO G
RB
070125 IN SW
IFT E
RA
POONAM CHANDRAJansky Fellow, NRAOUniversity of Virginia
•Synchrotron emission•Corrections to Inverse Compton•Inverse Compton important in X-rays only•IC important throughout the evolution•Role of IC in GRB Light curve
only the synchrotron model for the GRB afterglow and derive various parameters
spectrum due to IC scattering has the same shape as that of the synchrotron model.
ICmIC
c
ICm
p
ICm
ICIC
ICm
ICcIC
c
ICIC
FF
FF
;
;
2/12/
max
2/1
max
7.5 Jy;d7.3
0066.0
7.57.3 Jy;d7.3
0082.0
7.38.2 Jy;d8.2
0079.0
4.2
2/1
8/1
tt
F
tt
F
tt
F
IC
IC
IC
Inverse Compton Scattering flattens the X-ray light curve, at least in some GRBs.
Jet break in X-ray may get delayed beyond Swift observations.
It may be a major cause for the absence of jet break in X-ray bands.
CONCLUSIONS: GRB070125
•Radio scintillation detection•8 hours observation with VLA in 8 GHz•Mapped every 20 minutes
askpcm10kpcGHz10
25.25/3
3/205.3
15/6
SMDscrsrc
skpcm10s km 50GHz10
107.65/3
3/205.3
1
1-
5/64
SMvt ISSdiff
Size of the Fireball
cm107.5 17R
(Goodman 1997)
Poonam Chandra13th July 2005
SGR 1806-20
Giant flare on Dec 27, 2004
Detected by INTEGRAL, RHESSI, Wind Spacecraft, SWIFT, GMRT, VLA, ATCA etc.
80,000 counts/sec (RHESSI)
SGR 1806-20, Cameron, Chandra et. al. Nature
Poonam Chandra13th July 2005
27th December 2004 at 4:30:26.65 pm EST
Courtesy: NASA
Poonam Chandra13th July 2005
Precursor Spike Tail
Duration 1 sec 0.2 sec 382 sec
Temp 15 keV 175 keV 3-100 keV
Fluence (erg/cm2)
1.8x10-4 1.36 4.6x10-3
Energy (ergs)
2.4x1042 1.8x1046 1.2x1044
Poonam Chandra13th July 2005
GMRT observations of SGR 1806-20
•From January 4, 2005 to February 24, 2005
•Initially very frequently, almost everyday
•Snapshots, 40-60 minutes.
•Mostly in 240 and 610 MHz and in 1060 MHz at some occasions.
Poonam Chandra13th July 2005
Distance estimation of SGR 1806-20 from the HI absorption spectra
HI emission spectrum
Poonam Chandra13th July 2005
Source
HI absorption spectrum
Poonam Chandra13th July 2005
SGR 1806-20
Flux
den
sity
(Jy)
d
(kpc
) F
lux
dens
ity (J
y)
Brig
htne
ss te
mp
(K)
100
20
40
60
80
Velocity (km/s)- -50 0 50 100 150
0.2
0
0.4
0.6
0.8
0.08
0.04
2010
Lower limit d=6.4 kpc
Upper limit d=9.8 kpc
km/s 220
kpc 8
0
0
R
21cm HI spectrum
Poonam Chandra13th July 2005
Association with the heavy mass cluster and Luminous Blue Variable?
What kind of stars produce magnetars which forms SGRs?
COLLABORATORS
Claes Fransson (Stockholm Obs)Tanya Nymark (Stockholm Obs)Roger Chevalier (UVA)Dale Frail (NRAO)Alak Ray (TIFR)Shri Kulkarni (Caltech)Brad Cenko (Caltech)Bryan Cameron (Caltech)…and …. more
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